For many years voice telephone service was implemented over a circuit switched network commonly known as the public switched telephone network (PSTN) and controlled by a local telephone service provider. In such systems, the analog electrical signals representing the conversation are transmitted between the two telephone handsets on a dedicated twisted-pair-copper-wire circuit. More specifically, each telephone handset is coupled to a local switching station on a dedicated pair of copper wires known as a subscriber loop. When a telephone call is placed, the circuit is completed by dynamically coupling each subscriber loop to a dedicated pair of copper wires between the two switching stations.
More recently voice telephone service has been implemented over the Internet utilizing technology commonly known as Voice-over-IP or VoIP. Typical architecture for implementing VoIP includes a cable modem or other Internet Service Provider (ISP) device capable or providing Internet service at a subscriber's premises. A client device of a VoIP service provider, typically known as a media terminal adapter (MTA) or “line card” is coupled to the ISP device via a network and utilizes internet protocols for communication with the VoIP service provider infrastructure and other VoIP endpoints over the Internet. The line card also emulates a central office switch to support use of regular PSTN telephone handsets coupled to the premises twisted pair network may be used for initiating and terminating VoIP telephone calls.
Digital signal processing circuitry within the line card interfaces between the PSTN analog audio signals used for supporting operation of the PSTN telephone handset and both signaling messages exchanged with the VoIP service provider infrastructure and compressed digital audio frames exchanged with the remote VoIP endpoint over the Internet.
A common structure for enclosing multiple line cards (for supporting multiple PSTN lines) includes use of parallel “plug in” cards within a framed chassis. A problem associated with use of parallel “plug-in” cards for VoIP “line cards” is that the digital signal processing circuitry on a line card generates a significant amount of heat. In an environment where it is desirable to position multiple line cards outside of the subscriber premises, the line cards and associated systems must be housed within a sealed enclosure for protection against weather. This creates a situation where heat generated within the enclosure can exceed the operating limits of the electronic components of the line cards.
What is needed is a structure which provides improved heat dissipation properties and more specifically, to an electronic device comprising heat generating electronics populated on multiple circuit board “cards” within a sealed enclosure structure with improved heat dissipation properties.